Field of the Invention
The present disclosure relates to a polarization film having a black strip for applying to a patterned retarder type 3D display device. Especially, the present disclosure relates to a polarization film, as being combined with a patterned retarder on the outer side of the 3D display device, having a black strip for preventing the 3D cross-talk problem between the patterned retarder for the left-eye image and the patterned retarder for the right-eye image.
Discussion of the Related Art
Recently, thank to the advancement of the various video contents, the display devices which can selectively reproduce 2D images and 3D images are actively developed. For reproducing the 3D images, the display uses the stereoscopic technique or the autostereoscopic technique.
As one example of the glasses type, there is a 3D display device having a patterned retarder on the display panel. This 3D display device represents the 3D images using the polarization characteristics of the patterned retarder and the polarization glasses. Therefore, there is no cross-talk problem between the left eye image and the right eye image, and it ensure brighter luminescent so that the quality of the image is better than other type of 3D display device.
FIG. 1 is the perspective view illustrating the structure of a 3D display system having a patterned retarder according to the related art. The patterned retarder type 3D display system represents the 3D images using the polarization characteristics of the patterned retarder PR disposed on the display panel DP and those of the polarization glasses PG used by the observer.
Referring to FIG. 1, the patterned retarder type 3D display system includes a display panel DP representing 2D image or 3D image, a patterned retarder PR attached on the front surface of the display panel DP, and polarization glasses PG.
The display panel DP, as the device for displaying 2D video images and/or 3D video images, can include any one of the liquid crystal display device (or LCD), the field emission display (or FED), the plasma display panel (or PDP), the electroluminescence device (or EL) including the inorganic light emitting diode and the organic emitting diode (or OLED), and electrophoresis display device (or EPD). Hereinafter, we will explain the embodiments of the present disclosure focused on the case in which the display panel DP is the liquid crystal display panel.
The display panel DP includes liquid crystal cells disposed in matrix manner defined by the crossing structure of the data line and the gate line. The lower glass substrate SL of the display panel DP comprises the pixel arrays including the data lines, the gate lines, the thin film transistors, the pixel electrodes, and the storage capacitors. The upper glass substrate SU of the display panel DP comprises the black matrix, the color filter, and the common electrode. Each liquid crystal cell is driven by the electric field formed between the pixel electrode connected to the thin film transistor and the common electrode. Each inside surface of the upper glass substrate SU and the lower glass substrate SL has an alignment layer, respectively for setting up the pre tilt angle of the liquid crystal. Each outside surface of the upper glass substrate SU and the lower glass substrate SL has the upper polarization film PU and the lower polarization film PL, respectively.
The patterned retarder PR is attached on the outside surface of the upper polarization film PU of the display panel DP. The patterned retarder PR has a unit retarder corresponding to each line of pixel arrayed in the horizontal direction of the display panel DP. For example, one unit retarder can be defined as corresponding to the area of the pixels commonly connected to one gate line. Especially, the first retarder RT1 is formed as to be corresponding to the odd numbered lines of the patterned retarder PR, and the second retarder RT2 is formed as to be corresponding to the even numbered lines of the patterned retarder PR. The first retarder RT1 can transmit the first circular polarized light by retarding the phase of the light with +λ/4 (here, ‘λ’ is the wavelength of the light incident from the pixel array). The second retarder RT2 can transmit the second circular polarized light by retarding the phase of the light with −λ/4 (actually, +3λ/4). The light absorbing axis (or light transmitting axis) of the first retarder RT1 and the light absorbing axis of the second retarder RT2 are perpendicular each other.
For example, the first retarder RT1 of the patterned retarder PR can be the polarizing filter transmitting the left circular polarized light, and the second retarder RT2 of the patterned retarder PR can be the polarizing filter transmitting the right circular polarized light. In this case, the light of the video images represented on the odd numbered lines of the display panel DP can transmit the first retarder RT1 and then it becomes to the first circular polarized light (i.e., the left circular polarized light). Furthermore, the light of the video image represented on the even numbered lines of the display panel DP can transmit the second retarder RT2 and then it becomes to the second circular polarized light (i.e., the right circular polarized light).
The polarization glasses PG comprises a left glass window LG having the first polarizing filter P1 and a right glass window RG having the second polarizing filter P2. The first polarizing filter P1 has the same light polarization characteristic with that of the first retarder RT1 of the patterned retarder PR. At the same time, the second polarizing filter P2 has the same light transmitting axis with that of the second retarder RT2 of the patterned retarder PR. For example, the first polarizing filter P1 of the polarization glasses PG can be the left circular polarizing filter, and the second polarizing filter P2 of the polarization glasses PG can be the right circular polarizing filter.
With this structure, by representing the left images on the pixels relating to the first retarder RT1, and representing the right images on the pixels relating to the second retarder RT2, the 3D images can be implemented. In the 3D display system as shown in FIG. 1, by setting the polarized light characteristic of the left eye images different from that of the right eye images, the left eye image and the right eye images can be separately reached to the observer's left eye and right eye, respectively.
In the 3D display device having the film patterned retarder, as the left eye image and the right eye image are alternatively represented in the unit of pixel row, there are some cross-talk problems at the wide view angle along to the up-down directions. FIG. 2 is a cross sectional view along the cutting line A-A′ in FIG. 1 illustrating that the cross-talk problem occurring at the 3D display device as shown in FIG. 1.
Referring to FIG. 2, when observing the video data at upper side (or lower side) than the straight front direction, the left eye image L1 and the right eye image R1 can transmit through the first patterned retarder RT1, at the same time. As a result, the cross-talk problem is occurred in which the left eye image L1 and the right eye image R1 pass through the left glass window LG of the polarization glasses PG, at the same time. Even though, there is a black matrix BM at the border between the pixels in horizontal units, the black matrix BM does not have enough width to prevent the cross-talk problem.
In order to solve this cross-talk problem in the vertical view angle direction, some methods have been suggested. The first method is to make the width of the black matrix BM wider so that the wide view angle in which the cross-talk problem is not occurred can be ensured. FIG. 3 is the cross-sectional view illustrating the 3D display device in which the black matrix having wider width than the width of black matrix shown in FIG. 2.
Referring to FIG. 3, on the light path at which the right eye images R1 passes through the first retarder RT1, a black matrix BM having wider width is disposed so that the right eye image R1 passing through the first retarder RT1 can be blocked. Therefore, when an observer located at the straight front of the display device moves up side or down side somewhat, the cross-talk problems are not occurred. However, in this structure, in order to prevent the cross-talk problem more effectively, the black matrix BM should have remarkably wider width. As the width of the black matrix BM is getting wider, the aperture ratio at the front direction is getting lowered and then the brightness may be degraded or the correct color cannot be represented.
Like this, there is a trade-off relationship between the front aperture ratio and the cross-talk improvement. Furthermore, it is hard to find proper point therebetween. Therefore, required is a new method for ensuring the front aperture ratio and for enhancing the cross-talk problem at the same time.